1. Field of the Invention
The present invention relates to a pressure sensor comprising a diaphragm and a substrate processing apparatus comprising a pressure sensor.
2. Description of the Background Art
Conventionally, a fluid pressure sensor comprising a diaphragm between fluid and a pressure receiving device has been used. In such a pressure sensor, fluid flowing through a pipe presses the diaphragm, the pressure receiving device detects a pressing amount of the diaphragm, and a signal circuit converts the pressing amount into a pressure value.
In semiconductor processing apparatuses and various chemical plants, frequently used are chemicals with high corrosivity such as oxidizing power or the like or high permeability, and a fluid pressure sensor used in such a condition is needed to have extremely high chemical resistance and permeation resistance (penetration resistance). For example, fluorocarbon resin with high chemical resistance is used as material for forming a diaphragm. However, in a pressure sensor having high chemical resistance, if chemicals with high corrosivity and high permeability such as high-concentrated hydrofluoric acid (HF) are used, the lifetime of the pressure sensor is reduced to about one year and frequent calibrations are necessary, and these cause increase in running cost for a semiconductor manufacturing apparatus.
In the foregoing situation, with respect to a liquid contacting member contacting with chemicals having high corrosivity and high permeability (penetrating power), material for the member, arrangement of the pressure receiving device, or the like have been improved. For example, Japanese Patent Application Laid Open Gazette No. 7-72029 discloses a technique for improving chemical resistance, where a housing is made of material mainly composed of fluorocarbon resin and a pressure sensing part of a sensor device is made of anticorrosive material. The housing is divided into a part for a diaphragm and a part for holding the sensor device. Japanese Patent Application Laid Open Gazette No. 2002-310823 discloses a pressure sensor having a structure with excellent corrosion resistance to extend the lifetime, where a protective cap is attached to an end of a working rod and the end is housed in a diaphragm to which pressure of fluid is applied.
In the pressure sensor used in the semiconductor processing apparatus, the liquid contacting member such as the diaphragm or the like needs to have chemical resistance as described above and have an extremely low level of metal elution. Fluorocarbon resin such as PFA (a copolymer of tetra-fluoro-ethylene and per-fluoro-alkyl-vinyl-ether), PTFE (poly-tetra-fluoro-ethylene), PCTFE (poly-chloro-tri-fluoro-ethylene), and the like have high chemical resistance in comparison with other resin and satisfy the criteria of metal elution. Though these resin have high chemical resistance, their hardness tends to be affected by change of temperature. If mechanical properties change due to deterioration by micro cracks or plastic deformation caused by long pressing, an amount of deformation of the diaphragm relative to predetermined pressure changes, and consequently accurate pressure cannot be measured.
Corrosive chemical such as hydrofluoric acid or the like is not completely isolated by these resin. If adhesive between the pressure receiving device and the diaphragm is deteriorated by a small amount of chemical components (substances such as gas and the like) which transmit these resin, adhesion between the pressure receiving device and the diaphragm decreases, the pressure receiving device is damaged, whereby measurement reliability or measurement accuracy of the amount of deformation of the diaphragm is affected seriously.